The interaction between the tire and the road is crucial for determining the dynamic behavior of a road vehicle, and the road-tire contact forces are key variables in the design of traction, braking, and stability control systems. Traditionally, road-tire contact forces are indirectly estimated from vehicle-dynamics measurements (chassis accelerations, yaw-roll rates, suspension deflections, etc.). The emerging of the ldquosmart-tirerdquo concept (tire with embedded sensors and digital-computing capability) has made possible, in principle, a more direct estimation of contact forces. In this field - still in its infancy - the main open problems are the choice of the sensor(s) and the choice of the regressor(s) to be used for force estimation. The objective of this work is to present a new sensor-regressor choice, and to provide some preliminary experimental results, which confirm the validity of this choice. The idea is to use a wheel encoder and an accelerometer mounted directly in the tire. The measurement of the in-tire acceleration is transmitted through a wireless channel. The key innovative concept is to use the phase shift between the wheel encoder and the pulse-like signals provided by the accelerometer as the main regressor for force estimation.